The structure of the circular DNA molecular isolated from hepatitis B Dane particles and the mechanism of the Dane particle DNA polymerase will be analyzed using restriction endonucleases. Attempts will be made to infect tissue culture cells with Dane particles and Dane particle DNA. Infection will be tested for by immunofluorescence for HbsAg and HBcAg and radioimmunoassay for HBsAg. Patients with persistent hepatitis B virus infection and chronic active hepatitis will be treated with systemic interferon to determine the frequency and extent of the response of the infection and associated disease.